Q&A: How long will it take for my shares to double in value? The rule of 72...

​Hi Heather,
 
My name’s Grace. I recently started investing in stocks and shares and want to know the type of returns I should realistically expect? I’m especially interested in how long it will take for my money to double in value.
 
Thanks

Great question Grace, thank you for asking it.
 
I will start by telling you a little story. When I first started working, I didn’t believe in long-term investing on the stock market. My philosophy was that you buy shares at a good price and when the price has gone up high enough, you sell, take the profits and move on. You know, the buy low, sell high philosophy.
 
My philosophy has since changed. I believe you should buy shares and ideally never sell them except to manufacture a dividend while you are in retirement and I’ll give you two experiences that turned my thinking on this so radically.
 
In about 2006, I bought about $2,000 worth of Apple shares. The price at the time was $70-something. I sold a couple of years later when the price had trebled feeling like a complete winner. If I had held onto those shares they would now be worth about $30,000 (maybe more, it hurts too much to sit down and calculate the exact amount) AND I would have additionally enjoyed about 14 years of dividends from Apple which I would have reinvested back into the stock as I always do. Note that the price you see now shouldn’t be compared to the price I paid directly because Apple had a 7 for 1 stock split in 2014.
 
The way that works is that for every share you own, they split it into 7 shares and the price for each becomes one-seventh of what it was. The lower price is designed to make buying shares more palatable to smaller investors.
 
Anyhow, had I held the shares to retirement, I could have either benefitted from the dividends to support my living or sold them slowly for income to support my lifestyle in retirement (this is called manufacturing your own dividend). FYI, I’m only 36 so retirement is still a while away for me as I enjoy working and don’t plan to stop working for a while yet.
 
The second story is what happened to my pension savings from a job I had that had a defined contribution plan – this is a retirement plan that depends on how the stock market. Unlike the traditional workplace pensions the income in retirement is not based on a fixed formula.
 
Anyhow, I didn’t know much about pensions at the time but a colleague called Karen Matthey told me that even if I didn’t believe in pensions I should pay in up until the match “because it was free money” – I think the company matched contributions into the pension scheme up to a maximum of 3%. I didn’t even know what “up until the match meant” – I was 24 and clueless but I listened to her and did just that. By the time I left that job in 2012 I had just shy of £30,000 in my pension account and within 5 years that had grown to £60,000, that is, it had doubled. I didn’t expect this performance at all and it’s at this point that I started taking the whole investing long-term thing seriously.
 
Now, this made me curious to find how long it takes for an invested amount to double, which is exactly what you’re asking, Grace, and it’s at this point that I discovered what they call the rule of 72.
 
With the rule of 72, you take the investment return you expect, divide it into 72 and that’s how long it will take for you money to double. So, if you expect a 10% return, then your money will double in about 7 years. (72/10); if you expect a 7% return then you money will double in 10 years, it ‘s a very easy calculation.
 
Because my money doubled in 5 years, it’s also quick to calculate that I earned an average return of 14.4% (72/x = 5).
 
And keep in mind that I wasn’t invested in anything fancy: all my money in this pension was in a passive global equity tracker, it still is – and my old employer pays all the fees so I just let that pension pot sit there, I can’t touch it until I am at least 55.
 
If that money earns at least an average return of 10% (this is the actual historical stock market return), then over 21 years the money will double three times: 60k will double to 120k in 7 years (that’s by 2024, and it’s actually growing faster than this right now) which will double to 240k 7 years after that which will double to 480k 7 years after that (that’s by 2038 when I’ll be hitting 55). That’s insane, all from an initial 30k investment! After I figured this out I was annoyed at myself for not taking the stock market and pension investing more seriously and I’ve been making up aggressively for the last 3 years.
 
At the end of the day though, it’s not about crazy returns for me, it’s about making a commitment to investing healthy amounts monthly.
 
It’s very hard for most people, my younger self included, to believe that even £100/month invested over 30 or 40 years will amount to much but it is really surprising how these small amounts add up.
 
What stock market return should you expect?
 
There are no guarantees in the market, but the 10% average has been remarkably steady for a long time. That said, from year to year returns are very volatile. You will only get the average market return if you buy and hold, do not try to time the market.
 
Personally, I model my investments in excel based on a 7% gross return (gross return meaning the return before adjusting for inflation) this would be about 4% after inflation of 3%. My general reading suggests that expecting a return after inflation of 6% is realistic: my 4% net return is therefore not over optimistic.
 
If the experts are telling you to expect a real return of 6% that would make it a gross return of 9% because inflation tends to average 3%, using the rule of 72 you would expect your money to double every 8 years. Simples.
 
To ensure you end up with enough money in retirement, perhaps base your returns on a lower number so that either you end up with more money than you need or so that you can retire early because you reach your goal much sooner.
 
Key takeaways?
 

1. To calculate how long it will take your money to double, divide your expected return into 72.
2. You only get the average market return if you buy and hold.
3. Model your investment projections using a 7% gross return, which is 4% after inflation to be conservative.
4. Invest every month without fail, every little counts.
5. We haven’t covered it here but in addition to investing in equities, invest a portion in something lower risk like bonds or property.

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I hope this helps!
Heather

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